Bigger than Jupiter, a new planet in the constellation Cygnus is the largest discovered planet found orbiting two stars.
A team led by astronomers from NASA's Goddard Space Flight Center in Greenbelt, Maryland and San Diego State University (SDSU) in California, used NASA's Kepler Space Telescope to identify the new planet, dubbed as Kepler-1647b.
Kepler-1647 is 3,700 light-years away and approximately 4.4 billion years old, roughly the same age as Earth. The stars are similar to the sun, with one slightly larger than our home star and the other slightly smaller. The planet has a mass and radius nearly identical to that of Jupiter, making it the largest transiting circumbinary planet ever found.
Planets that orbit two stars are known as circumbinary planets, or sometimes "Tatooine" planets, after Luke Skywalker's home world in "Star Wars." Using Kepler data, astronomers search for slight dips in brightness that hint a planet might be passing or transiting in front of a star, blocking a tiny amount of the star's light.
William Welsh, a SDSU astronomer and co-author said, "Finding circumbinary planets is much harder than finding planets around single stars. The transits are not regularly spaced in time and they can vary in duration and even depth."
Another co-author and astronomer Jerome Orosz explained, "It's a bit curious that this biggest planet took so long to confirm, since it is easier to find big planets than small ones. But it is because its orbital period is so long."
The planet takes 1,107 days - just over three years - to orbit its host stars, the longest period of any confirmed transiting exoplanet found so far.
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The planet is also much further away from its stars than any other circumbinary planet, breaking with the tendency for circumbinary planets to have close-in orbits.
Interestingly, its orbit puts the planet within the so-called habitable zone-the range of distances from a star where liquid water might pool on the surface of an orbiting planet
Like Jupiter, however, Kepler-1647b is a gas giant, making the planet unlikely to host life. Yet if the planet has large moons, they could potentially be suitable for life.
"Habitability aside, Kepler-1647b is important because it is the tip of the iceberg of a theoretically predicted population of large, long-period circumbinary planets," said Welsh.
This research has been published in Astrophysical Journal.